The practical significance of OLEDs, which were only developed a few years ago, as lamps has been increasing for some time, as their light output and efficiency has been steadily increasing. So, for example, it is already possible to produce OLEDs with an efficiency of 35 lm/Watt and even up to more than 60 lm/Watt with a brightness of 1000 cd/m2 and a service life of 100,000 hours. The OLEDs are applied in very thin layers of for example only a few nm to a flat carrier. Thin, plate-like, rectangular substrates such as glass plates are for example for the most part used as carriers. In applications of lamps based on OLEDs known so far, these have consequently been consistently considered as a flat light source, as the available OLEDs on plate-shaped carriers of the above-mentioned type are taken as the starting point.
Typical applications for such OLEDs as multi-layer, flat light source on rectangular, rigid carriers are described in DE 60306720 T2. An OLED layer, two electrode layers and an encapsulating covering are applied to a transparent carrier. The latter is provided at one end with contacts on tongue sections, which can be plugged into a type of socket strip with openings so that contacting can take place. The disadvantage of these known OLEDs is on the one hand the fact that the OLED is defined by the manufacturer as a flat, even, plate-shaped light source on a rectangular carrier, and thus there are already limitations in the use of such a light source for the subsequent user. On the other hand, the OLEDs of this type known until now entail technical problems in the regions of the edges of the plate-shaped OLED carrier, as there is a limit line of the very thin layer of the organic light-emitting diode, which can result in irregularities in the light radiation. For example, the flow of the charge carriers can be disrupted in this edge region. Damage to the light-emitting layer has even occurred in this edge region in conventional OLEDs on rectangular carrier. The encapsulation of the organic light-emitting layer is generally necessary, as the organic materials are sensitive to moisture and oxygen.
DE 603 06 722 T2 describes a semiconductor light source for illuminating a region, with a rigid carrier, a flexible substrate which is fixed to the carrier, an organic light-emitting diode layer which is situated on the flexible substrate and has a first and a second electrode for transmitting electrical energy to the OLED layer, an encapsulated covering on the OLED layer, a first and second conductor which are connected electrically to the first and second electrodes and extend beyond the encapsulating covering, and with a connector which is connected to the rigid carrier for removable accommodation in a holder. According to a possible variant of the solution described in this document, it is provided for the even, rectangular carrier which bears the OLED layer to be provided with a socket which has a holder, the dimensions of which are compatible with those of a conventional holder, so that a conventional lamp can be replaced with one created in such a manner based on OLEDs.
A variant likewise described in the above-mentioned document provides for the OLED layer to be applied on a flexible substrate, for example in the form of a film, which can then where necessary be wound in a spiral manner on a for example cylindrical carrier consisting of glass, as a result of which a cylindrical, tube-like, OLED-based lamp is produced, which can in turn be provided with a holder and is then a lamp which can be exchanged with a conventional light bulb or fluorescent tube. In this variant, however, the film which acts as the substrate is thus first coated with the layers necessary for the functioning of the OLED, and only then can such a substrate (the film) which is coated with OLEDs, as it is flexible, be applied to a cylindrical carrier in a further production step. The disadvantage of the OLEDs which are applied to flexible films as the carrier is the fact that the flexible plastic substrate is too permeable to oxygen and air humidity and therefore the organic layer is not sufficiently protected in this case.
The use of very thin glass has also been proposed in order to create a carrier for the organic layer which is flexible to a certain extent. The thin glass is however difficult to process, and also the conventionally used anode material, for example, indium tin oxide, is a hard material and therefore brittle, so that damage to the electrode layer can occur when rolling out such a carrier.
A third variant described in DE 603 06 722 T2 provides for a rectangular, flat, even carrier which is provided with a frame to be produced in turn first, which is coated with the OLED layer and the electrodes, but in miniaturised form, and then for this even, rectangular OLED element, which is virtually already a lamp, to be introduced into the cavity of a glass flask in the form of a light bulb, which is provided with a socket with a holder, in order in this manner to replace the filaments of the light bulb and create an OLED-based light bulb. This procedure however requires after the production of a virtually conventional OLED on a conventional flat carrier the additional step of introducing this element into a hollow body, so that the production process is comparatively complex. A further disadvantage of this solution consists in that only one OLED with a comparatively small area which is effective for light output is used. As the luminosity of the lamp is proportional to the OLED area, only a small light output is obtained also.
Although the solution variants described in DE 603 06 722 T2 include the basic idea of producing lamps using organic light-emitting diodes, which imitate the appearance of a conventional lamp such as the classical light bulb for example and can be used in similar applications, the OLED layer and the electrode layers are always applied to a flexible substrate (in the form of a film) first and only then, in a second step, is this flexible substrate applied, for example adhesively bonded, to a rigid carrier with for example the shape of a cylinder or a truncated cone. The above-described disadvantages of the flexible substrate are thereby retained. It is furthermore necessary to provide the OLED layers on the flexible carrier with a protective layer (to encapsulate them).
This is where the present invention applies. The object of the invention is, proceeding from the above-mentioned prior art, to create an OLED-based lamp which does not have the disadvantages mentioned, allows more versatile applications and in the process allows efficient series production.